Raman scattering and electron-phonon coupling in mized-valent and superconducting compounds

Polarized Raman spectra of mixed-valent Sm_0.75Y_0.25S are presented and compared with those of semiconducting SmS and superconducting YS and TiN. The spectra are explained in terms of cluster deformabilities which also govern the phonon anomalies. The existence of a breathing Γ₁⁺ deformability of Sm in Sm_1?xY_xS, of S in YS, of N in TiN and a quadrupolar Γ₁₂⁺ deformability of N in TiN is demonstrated. The relationship between these results and the microscopic theory is discussed.